The structural gene for the yeast protein iso-1-cytochrome will be isolated from a digest of high-molecular weight yeast DNA cleaved by eco RI endonuclease. The isolated gene will be joined to a bacterial replicon and replicated extensively by growth of the chimeric DNA molecule in E. coli. In vivo cyc-1 gene expression will be studied by hybridizing pulse-labeled RNA to an excess of cytochrome c gene denatured DNA. By this procedure we will determine whether the rate of cytochrome c m-RNA synthesis is changed during oxygen induction of mitochondrial biogenesis and during release from glucose repression. When the purified gene is available, an in vitro transcription system will be set up to copy cyc-1 gene with yeast RNA polymerase II. Regulatory factors, both positive and negative, will be tested in the in vitro system. Bibliographic references: Hopper, A.K. and B.D. Hall (1975) Control of Yeast Sporulation by the Mating-type Locus. Spores VI, pp. 138-146. American Soc. for Microbiology. Hopper, A.K. and B.D. Hall (1975) Mating-type and Sporulation in Yeast. I. Mutations which Alter Mating-type Control over Sporulation. Genetics 8:41-59.